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Sequencing study lifts veil on wine’s microbial terroir


Davis, California, USA
November 25, 2013

Vineyard seen with the sky on the horizon

It’s widely accepted that terroir — the unique blend of a vineyard’s soils, water and climate — sculpts the flavor and quality of wine. Now a new study led by UC Davis researchers offers evidence that grapes and the wines they produce are also the product of an unseen but fairly predictable microbial terroir, itself shaped by the climate and geography of the region, vineyard and even individual vine.

Results from DNA sequencing revealed that there are patterns in the fungal and bacterial communities that inhabit the surface of wine grapes, and these patterns are influenced by vineyard environmental conditions. The findings appear online this week in the Early Edition of the Proceedings of the National Academy of Sciences.

“The study results represent a real paradigm shift in our understanding of grape and wine production, as well as other food and agricultural systems in which microbial communities impact the qualities of the fresh or processed products,” said Professor David Mills, a microbiologist in the Department of Viticulture and Enology and Department of Food Science and Technology.

He noted that further studies are needed to determine whether these variations in the microbial communities that inhabit the surface of the grapes eventually produce detectable differences in the flavor, aroma and other chemically linked sensory properties of wines.

The study co-authors suggest that by gaining a better understanding of microbial terroir, growers and vintners may be able to better plan how to manage their vineyards and customize wine production to achieve optimal wine quality.

Sequencing grape microbes
To examine the microbial terroir, the researchers collected 273 samples of grape “must” — the pulpy mixture of juice, skins and seeds from freshly crushed, de-stemmed wine grapes.

The must samples were collected right after crushing and mixing from wineries throughout California’s wine-grape growing regions during two separate vintages. Each sample, containing grapes from a specific vineyard block, was immediately frozen for analysis.

The researchers used a DNA sequencing technique called short-amplicon sequencing to characterize the fungal and bacterial communities growing on the surface of the grapes and subsequently appearing in the grape must samples.

They found that the structure of the microbial communities varied widely across different grape growing regions. The data also indicated that there were significant regional patterns of both fungal and bacterial communities represented in Chardonnay must samples. However, the Cabernet Sauvignon samples exhibited strong regional patterns for fungal communities but only weak patterns for bacterial communities.

Further tests showed that the bacterial and fungal patterns followed a geographical axis running north-south and roughly parallel to the California coastline, suggesting that microbial patterns are influenced by environmental factors.

Taken together, these and other results from the study reveal patterns of regional distributions of the microbial communities across large geographical scales, the study co-authors reported.

They noted that it appears that growing regions can be distinguished based on the abundance of several key groups of fungi and bacteria, and that these regional features have obvious consequences for both grapevine management and wine quality.

Collaborating with Mills were graduate student Nicholas Bokulich of the UC Davis Department of Viticulture and Enology; John Thorngate of Constellation Brands Inc.; and Paul Richardson, CEO of MicroTrek Inc., a company founded to provide microbial mapping services to help vintners understand this phenomenon.

Constellation Brands Inc. provided in-kind support for the study through sample and metadata collection.

Funding for the study was provided, in part, by the American Wine Society Educational Foundation Endowment Fund, the American Society of Brewing Chemists Foundation and the Wine Spectator.

STUDY

Geographical region and climate predict wine grape microbial populations
by Nicholas A. Bokulich, John H. Thorngate, Paul M. Richardson, David A. Mills

Significance
We demonstrate that grape-associated microbial biogeography is nonrandomly associated with regional, varietal, and climatic factors across multiscale viticultural zones. This poses a paradigm shift in our understanding of food and agricultural systems beyond grape and wine production, wherein patterning of whole microbial communities associated with agricultural products may associate with downstream quality characteristics. Elucidating the relationship between production region, climate, and microbial patterns may enhance biological control within these systems, improving the supply, consumer acceptance, and economic value of important agricultural commodities.

Abstract
Wine grapes present a unique biogeography model, wherein microbial biodiversity patterns across viticultural zones not only answer questions of dispersal and community maintenance, they are also an inherent component of the quality, consumer acceptance, and economic appreciation of a culturally important food product. On their journey from the vineyard to the wine bottle, grapes are transformed to wine through microbial activity, with indisputable consequences for wine quality parameters. Wine grapes harbor a wide range of microbes originating from the surrounding environment, many of which are recognized for their role in grapevine health and wine quality. However, determinants of regional wine characteristics have not been identified, but are frequently assumed to stem from viticultural or geological factors alone. This study used a high-throughput, short-amplicon sequencing approach to demonstrate that regional, site-specific, and grape-variety factors shape the fungal and bacterial consortia inhabiting wine-grape surfaces. Furthermore, these microbial assemblages are correlated to specific climatic features, suggesting a link between vineyard environmental conditions and microbial inhabitation patterns. Taken together, these factors shape the unique microbial inputs to regional wine fermentations, posing the existence of nonrandom “microbial terroir” as a determining factor in regional variation among wine grapes.

About UC Davis
For more than 100 years, UC Davis has been one place where people are bettering humanity and our natural world while seeking solutions to some of our most pressing challenges. Located near the state capital, UC Davis has more than 33,000 students, over 2,500 faculty and more than 21,000 staff, an annual research budget of nearly $750 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges — Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science. It also houses six professional schools — Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.

 



More news from: University of California, Davis


Website: http://www.ucdavis.edu

Published: November 27, 2013



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